1. Field of the Invention
The invention relates to an in-vitro method of identifying reagins present in the blood serum of allergen sensitized vertebrates, including humans.
2. Brief Description of the Prior Art
Reagins are complex organic compounds belonging to the class of immunoglobulins known as immunoglobulin E (generally referred to for convenience as "IgE"). More specifically reagins are a group of type IgE proteins found in the blood serum of vertebrates, following their sensitization by exposure to an allergen or allergens. Sensitization comprises the endogeneous production of the reagin by the vertebrate, stimulated by the presence of the allergen. The mechanism for reagin production is a matter for speculation. The endogeneously produced reagin may be characterized in part by its antibody-like activity, i.e., its specific reactivity in binding at epitopic sites on the counterpart allergen which is the source of its own genesis. The reagin also generally has a propensity to attach to living cells throughout the body of the host vertebrate. When the counterpart allergen is reintroduced into the previously sensitized host vertebrate, an allergen-reagin reaction takes place usually with a consequential anaphylactoid type of immune reaction. The latter results primarily from a rupture of eosinophils and basophils having attached reagins - allergen complex. Rupture of the cells releases histamine, slow-reacting substance of anaphylaxis, eosinophil chemotaxic substance, lysosomal enzymes and other compounds which result in an allergic reaction in the host vertebrate. Allergic reactions include anaphylaxis, urticaria, hay-fever, asthma and like clinical manifestations.
To avoid allergen-reagin reactions in a sensitized vertebrate, one hopefully identifies reagins in the blood serum of the vertebrate and then precautions may be taken to limit exposure of the sensitized individual to allergens corresponding to the identified reagin or reagins or by desensitizing the individual to specific allergens.
In view of reagin antibody activity, prior art in-vitro methods of identifying reagins in blood serum have been based, empirically, on the known and classic immunological relationship which exists between an antigen and its corresponding antibody. However, such prior art methods have not been entirely satisfactory in regard to reagin identification for a number of reasons. First, allergens, which are in essence protein substances foreign to the chemistry of a given vertebrate, apparently stimulate the production of relatively small quantities of reagin in comparison for example to the production of antibody to disease antigens. The smaller production of reagin complicates its detection and identification in the complex mixture comprising blood serum.
Additionally, the majority of native allergens possess a plurality of allergenic determinants and when introduced into a vertebrate will provoke or elicit a mixed plurality of reagins instead of a single reagin. The mixture of reagins will differ from each other in their physicochemical and biological properties, complicating further identification of the reagin entity. Some of the minor reagin compounds elicited in the mixture may be in such low concentrations that they are not detectable by conventional physicochemical techniques.
Secondly, since most IgE material isolated from host organisms has been found to be a heterogeneous mixture of structurally similar but diverse proteins, and a specific reagin may in fact be a mixture of different reagin molecules, any in-vitro detection method based on binding of the reagin with an allergen may depend for accuracy on a protocol which may or may not account for all of the diverse reagin molecules and not just a portion of the mixture.
In addition, it will be appreciated that since immune sera contains reagins which will bind to their corresponding allergens with varying degrees of avidity, strong positive allergen-reagin reactions may not always be obtained in reasonable times. Further, the physical nature of the reagin mixture might be expected to affect the strength of any interaction or binding of reagin which may occur.
It has also been recognized that IgE materials do not behave in the same way as, for example, IgM or IgG the protective antibodies produced by an organism to counteract antigens related to diseases. In the latter process, the host organism may continue to produce "protective" types of antibody even after the disease state or entity has been eliminated, thereby obtaining immunity to re-infection. In contrast, in the case of allergy whose physical manifestation of the allergic response is the binding of the allergen with the reagin, no immunity is necessarily conferred. When the binding reaction occurs, cellular damage occurs wherein substances such as histamine are released to affect allergic target tissues. The binding reaction will occur during every subsequent re-introduction of allergen into the host organism.
Clearly, although there are apparant analogies between the classical immunological antigen-antibody relationship and the more specific allergen-reagin process, there are also subtle and marked differences. It is these differences which suggest that the prior art empirical use of antigen-antibody in-vitro identification procedures to identify allergens-reagins may have been misplaced and accounts for the inaccuracies which have been observed (lack of avidity, specificity) and the lack of sensitivity.
Because of the dissatisfactions with the prior art in-vitro methods of determining and identifying reagins in blood serums, the most widely employed methods of determining reagins present in the blood serum of allergen sensitized vertebrates (and thereby a differential diagnosis of atopic or anaphylactic allergy) are the in-vivo skin and provocation test methods. These invivo test methods are also lacking in complete satisfaction. They are time consuming, inconvenient to patients and not without serious risk. The potential for anaphylaxis upon exposure of the patient to allergens is a real hazard.
Like the prior art in-vitro methods for identifying reagins, the in-vivo methods are also inaccurate to a degree. The allergen-reagin reaction physical manifestations observed in skin-testing may be affected by subjective influences such as an allergic threshold in individual body resistance to allergic response. Emotional factors in the individual undergoing testing can also affect the allergic response.
In summary the prior art methods, both in-vitro and in-vivo, for identifying reagins in the blood sera of vertebrates have not been entirely reliable, accurate or safe for the variety of reasons described above. The method of the present invention is an improvement over in-vitro testing, based on the adsorption of an allergen on a water-insoluble carrier particle and agglutination of the particles in the presence of the reagin counterpart of the adsorbed allergen.
There are a number of advantages associated with the method of our invention. A major advantage resides in the capability of performing allergen identification testing in the physician's office on a simple, economical and rapid basis. The use of the patient's blood serum in an in-vitro test method obviates the hazards associated with conventional skin-testing and provocation test proecedures (risk of anaphylaxis). This is particularly advantageous where the very young, elderly and debilitated individual is the object of testing. Other advantages include more stable reagents with less associated hazards and which require less training in their use than those associated with, for example, the radioallergo-immunosorbent test (RAST) which employs radioactive labelled reagents. The reagents used in the method of the invention also have longer shelf-lives than radio-active labelled reagents and are safer to use.
The method of the invention also requires only small blood serum samples for testing (less than 5.0 ml), providing the patient with considerably decreased discomfort and loss of time. Once the blood sample is obtained the patient need not wait for results. Automation of the procedure will enable the physician to increase the number of patents he can diagnose in a given time period.
Because the method of the invention measures specific IgE it enables the physician to monitor allergy therapy by monitoring serum IgE levels. This is a very sensitive monitor. In contra-distinction skin test results fluctuate rapidly over short periods of time depending on the physical state of the patient. The method of the invention is more consistent and repeatable than skin-testing because it comprises monitoring serum components which are less affected by the patient's physical condition.